1. Field of the Invention
The present invention relates to a sheet folding apparatus that performs folding processing on a sheet, an image forming apparatus equipped with the sheet folding apparatus, and an image forming system.
2. Description of the Related Art
A conventional image forming system is known that is equipped with a sheet folding apparatus that performs folding processing on a sheet on which an image is formed by an image forming apparatus. A sheet folding apparatus is known that performs folding processing in which a bend formed on a sheet in a conveying path is nipped and conveyed between a pair of folding rollers that is a pair of roller members to form a folded part.
A sheet folding apparatus described in Japanese Patent Application Laid-open No. 2007-277006 includes a pair of upstream rollers and a pair of downstream rollers that are disposed along a sheet conveying direction and that hold a part of a sheet to apply conveying force to the sheet. The sheet folding apparatus also includes a pair of folding rollers that forms a folded part on the sheet by nipping a turned-back portion formed between the pair of upstream rollers and the pair of downstream rollers by bending the sheet. The following describes how the sheet folding processing is performed. The pair of upstream rollers and the pair of downstream rollers each hold a part of the sheet, and the pair of downstream rollers applies conveying force to the sheet to reverse the sheet upstream in the sheet conveying direction, thereby forming a turned-back portion on the sheet between the pair of upstream rollers and the pair of downstream rollers. The turned-back portion thus formed is then guided to and nipped between the pair of folding rollers to form a folded part on the sheet.
When a stiff sheet such as thick paper is used, for example, poor folding may occur because the turned-back portion formed by reversing the pair of downstream rollers cannot be nipped between the pair of folding rollers depending on the thickness or the type of the sheet.
A sheet folding apparatus described in Japanese Patent Application Laid-open No. 2006-52074 includes a pushing member that is movable between a pushing position at which the pushing member pushes a turned-back portion of a sheet in the thickness direction of the sheet toward a nip between the pair of folding rollers, and a retracted position at which the pushing member is retracted from the pushing position.
The pushing member moved from the retracted position to the pushing position pushes the turned-back portion into the pair of folding rollers, so that the turned-back portion is surely guided into the nip between the pair of folding rollers. Providing such a pushing member enables appropriate folding processing.
A sheet folding apparatus, for example, can be smaller in size when it is not provided with a conveying path dedicated for folding processing inside the apparatus. This is possible when the sheet folding apparatus is provided with a pair of folding rollers in a conveying path that conveys a sheet to an apparatus such as a sheet post-processing apparatus disposed downstream of the sheet folding apparatus. With this configuration, when the pair of folding rollers does not form a folded part, the sheet folding apparatus switches a direction in which the leading end of the sheet proceeds by a bifurcating claw, or the like, from a direction from the pair of upstream rollers to the pair of downstream rollers to a direction from the pair of upstream rollers to the pair of folding rollers. The sheet folding apparatus then needs to change the course of the sheet so that the leading end of the sheet proceeds from the pair of upper rollers through the pair of folding rollers to a conveying path disposed downstream of the pair of folding rollers.
Providing both the pressing member and the bifurcating claw in the sheet folding apparatus to guide the turned-back portion toward the pair of folding rollers or to change the course of the sheet increases the number of parts and requires additional installation space for the members, thereby undesirably increasing the size of the apparatus.
In view of the above, there is a need to provide a sheet folding apparatus that can guide a turned-back portion of a sheet toward a folded part forming unit, and can change the course of the sheet by changing the direction of the leading end of the sheet without increasing the size of the apparatus, an image forming apparatus equipped with the sheet folding apparatus, and an image forming system.